Indttstrie axtiengesellschaft



- Patented June 14 1927 UNITED STATES v 1,63 areNT OFFICE.

' ALFRED MILLER, or DESSAU IN ANHALT, GERMANY, ASSIGNOB no I. G. rename INDUSTRIE AxTmNeEsELLscHArr, or rRANKronr-omrnE-mm, GER-MANY.

iunrnon or imxmerno'roenarigrc corms B Y REvEnsAL.

No Drawing. Application flled september 23, 1925, Serial No. 58,191, and iii Germany March 21, 1925.

The present invention relates to a method of making photographic copies of prints, drawings and the like by reversal.

In the art of making photographic copies 5 of line drawings, printed text and the like,-

it wvas heretofore practically necessary to could be printed. Attempts have been made to produce posi- 1 tives directly, i. e. without first making negatives, but the methods in-this direction have not been a practical success. As a general rule they are tootedious or too unreliable.

simple and reliable method of directly making positives by .reversal.

The invention is based 0 salts upon the gelatines. If, for instan ce, a ferric chloride solution is allowedto act upon a ne ative produced upon a silver bromide ge atine, the solution penetrates those places'which are free of: silver and effects a tanning action. However, at theplaces covered by a silver de osit, the ferric chloride penetrates comparatively slowl because of the reduction of ferric chlori e to ferrous chloride as the result of the reaction with the metallic silver which isre-converted to silver salt. I

.- It was found that the difference between the relative rates of penetration may be in- I creased by the addition of potassium ferricyanide, to the ferric chloride solution. To

facilitate the conversion of the metallic sil ver deposit into a silver salt some potassium bromide may be further added.

When a freshly developed and rinsed 40 negative produced upon a silver bromide.

'gelatine plate is' subjected, while being a tated as little as possible, to the action of life solution just described. a well-known reaction takes place immediately at the places 4 colored by the silver deposit resulting in a superficial precipitate of Berlin blue, which for a brief period protects the underlying layer of gelatine against the penetration of the ferric chloride, whereas at the places where there is no deposit of silver, thelatter is free to penetrate and effect its tanning action.

When the su blue is now was edofi with cold. water, it

'mordant action of the ferric chloride. At prepare'a negative from which the positive The object of the present invention is 9.

upon the well known hardening action ofcertain metallic chloride-potassium ferricyanide bath with a affect the whiteness of the back-ground, is

erficially adhering Berlin can be observed that it readily adheres to the places where there was no silver deposit .ture of the negative is bleached while the remaining part is coloured, which epresents a totalreversion of the picture. This silver salts formed by the reaction with the metallic silver deposit may be removed in wellknown manner. A i r Since the Berlin blue spreading over; the unexposed areas and deposited thereon is derived from the places where metallic silver Q was deposited, as described, it would be difficult to deposit a sufiicient amount thereof on larger unexposed areas. This can be readily remedied by followingup the ferric 8o bath of potassium ferrocyanide of suitable degree of co c'entration, which causes at the unexposed p aces, where ferric chloride has penetrated into the layer of gelatine, the original formation of Berlin blue. At the places originally containing a silver deposit and subsequently covered with a precipitate of Berlin blue the excess of ferric chloride, due to the action of the potassium ferrocyanide bath with the resulting formation of fresh Berlin blue, is at once prevented from\ penetrating and hardening theunderlying" gelatine layer, whereby a subsequent hardenmg of these places, which might tend to precluded.

Best suited for carrying out theinvention I I are unhardened emulslons of medium thicknessand of steep gradation. By application ofifilrns or transparent paper thejreproduced print or drawlng appears correct when viewed through the support or *carrier. With an opaque support it is necessary to use an inverting prism or its equivalent to obtain lateral inversion, of the image, as iswell understood. As an alternative the ic-- ture may be made in the manner descri d and the support may be made transparent so that the picture may be viewed throu h it. The process may be carried out as fo ows: The developed negative is well rinsed and then immersed for the period of about 20 seconds, while avoiding as much as possible movement thereof in the bath, in a solution containing approximately 1000 parts water, 100 parts potassium ferricyanide, 20 parts ferric chloride, 15 parts potassium bromide. Then the negative is taken out and at once rinsed under a spray, then placed in a water bath and fixed and then again placed in water. Or, after the treatment with the solution, the negative may be placed into a bathof a 25 per cent potassium ferrocyanide solution and then rinsed and fixed as before. When the layer is sufliciently thin and the tanning action has reached the bottom the unhardened places may be washed off in warm water, whereupon the tanned places, i. e. the areas representing the text of the lines of a drawing, with dyes or the visible effect.

While in the foregoing reference was made to iron salts other salts may find applicamay be specially treated like to accentuate the tion, for instance uranium salts, which have an analogous action.

To intensify the hardening effect there may be added other compounds, such as formaldehyde or quinone- It is also sometimes desirable to use other metal salts, for

instance uranium salts, in addition to the iron salts. The visible effect produced and representing the original may be given a greater covering power by a suitable subsequent treatment. The blue picture hereinbefore referred to may be suitabl toned, for

1 instance by means of tannic aci Also the presence of dyes, especially mordant dyes, in the hardening or fixingbath act in the same manner.

I claim,

1. In a method of making photographic reproductions, the ste which consists in treating a freshly deve oped silver negative with an aqueous solution containing ferric chloride and potassium ferri-cyanide.

2. In a method of making photographic reproductions, the step which consists in treating a freshly developed silver negative with an aqueous solution containing ferric chloride, potassium ferri-cyanide and potassium bromide.

3. In a method of making photographic reproductions, the steps which consist in treating a freshly developed silver negatlve with an aqueous solution containing ferric chloride, potassium ferri-cyanide and potassium bromide, wherebg a removable protective layer is formed y reaction with the silver deposit at the places which'have been exposed to light, and removing the said layer.

4. In a method of making photographic reproductions the steps which consist in treating a freshly developed silver negative with an aqueous solution of ferric chloride and potassium ferricyanide, causing a tanning of the portions'not covered by a silver deposit and reacting with the silver deposit to form upon the portions'covered thereby a loosely adhering layer of'Berlin blue and v rinsing the negative thus treated, thereby removing the Berlin blue from its places, of formation and spreading it over the tanned portions.

5. In a method of making photographic reproductions the steps which consist in treating a freshly developed silver negative with an aqueous solution of ferric chloride, potassium ferricyanide and potassium bromide, rinsing the negative after treatment and subjecting it to the action of a potassium ferrocyanide solution.

6. In a method of making photographic reproductions the step which consists in treatinga freshly developed silver negative with a solution of about 100 parts of otassium ferricyanide, 20 parts ferric ch oride and 15 parts potassium bromide in about 1000 parts of water.

7. In a method of making photographic reproductions the steps which consist in treating a freshly developed silver negative with 'a-solution of about 100 parts potassium ferricyanide, 20 parts ferric chloride and 15 parts of potassium bromide in about 1000 parts ofwater and subsequently bathing the negative in an approximately 25 per cent solution of potassium ferrocyanide.

In testimony whereof, I aflix my signature.

DR. ALFRED MILLER. 

